HUMAN NERVOUS SYSTEM | NERVOUS SYSTEM PARTS AND FUNCTIONS

HUMAN NERVOUS SYSTEM | NERVOUS SYSTEM PARTS AND FUNCTIONS

May 1, 2018 Off By Free Online Notes

What is Human Nervous System? The Human Nervous System is a type of centralized nervous system’, which includes various parts i.e Central Nervous System and Peripheral Nervous System. Let’s discuss in detail various parts of nervous System are as under;

PARTS AND FUNCTIONS OF HUMAN NERVOUS SYSTEM

The Human nervous system consists of two parts.

  • Central Nervous System
  • Peripheral Nervous system

CENTRAL NERVOUS SYSTEM (CNS)

The central nervous system has two parts;

  • Brain
  • Spinal cord.

Both the brain and spinal cord are protected in three ways:

i) Cranium: Cranium which is part of a skull, protects the brain and neural arches of vertebrae. The vertebral column protects the spinal cord.
ii) Meninges: Beneath the cranium, the brain and spinal cord are protected by a triple layer of meninges.
iii) Cerebrospinal fluid (CSF): Between the layers of meninges, the cerebrospinal fluid (CSF), similar in composition to blood plasma, bathes the neurons of the brain and spinal cord and it cushions against the bumps and jolts.
Both brain and spinal cord are hollow. The spinal cord has central canal and brain has many cavities (ventricles) filled by CSF.

BRAIN

The brain can be divided into forebrain, midbrain and hindbrain.

1. Forebrain

The forebrain is further divided into three functional parts:
i) the thalamus, ii).the limbic system and iii) the cerebrum.
Thalamus: Thalamus carries sensory info to the visceral brain and neural structure. the data includes sensory input from sensory system and visual pathways from the skin and from among the body.

Limbic system: The limbic system is located in between tthe thalamus and cerebrum. Limbic system work together to produce our most basic and primitive emotions, drives, and behaviours, including fear, range, tranquility (calmness, peace of mind), hunger, thirst, pleasure and sexual  responses. Portion of limbic system is also important in the formation of memories. The limbic system consists of hypothalamus, the amygdale, and hippocampus, as well as nearby regions of cerebrum.
a)        Hypothalamus: The hypothalamus through its hormone production  and neural connections acts as a major coordinating centre controlling body temperature, hunger, the menstrual cycle, water balance and the sleep-wake cycle.
b)         Amygdale: In the amygdale, cluster of neurons produce sensation    of pleasure, punishment or sexual arouser when stimulated. It is also involved in the feelings of fear and rage.
c)         Hippocampus: Hippocampus plays an important role in the formation of long term memory, and thus is required for learning.
Cerebrum: Cerebrum is the largest part of the brain and is divided into two halves, called cerebral hemispheres. The left cerebral hemisphere controls ‘the right side of the body, and right cerebral hemisphere controls the left side of the body. The two cerebral hemispheres communicate with one another by means that of an outsized band of axons, referred to as nerve tract. Tens of billions of neurons are packed into this half. The outer region, the cerebral mantle, forms folds referred to as convolutions, that greatly increase its area. This half receives sensory info, processes it, stores some in memory for future use, direct voluntary movements, and ar liable for the poorly understood method that we have a tendency to decision thinking.  The cerebral mantle performs following functions:
i) It contains primary sensory areas where signals originating in  sensory organs such as eyes and ears are received and converted into subjective impressions, such as light and sound. Nearby association areas interpret this information.
ii) This area is also involved in speech and also receives and interprets sensations of touch from all parts of the body.
iii) This area is also a centre for sending impulses to voluntary muscles, controlling movements.
iv)        This is also involved in intelligence, reasoning and judgement.

2. Midbrain

Midbrain is reduced in humans, and it contains auditory relay centre and centers that control reflex movements of eyes. Midbrain contains reticular formation, which is a relay centre connecting hindbrain with the forebrain.  Reticular formation is very important in screening the input information, before they reap hind brain centers.

3. Hindbrain

Hindbrain includes the medulla, pons , nd cerebellum.
Medulla: Medulla controls several automatic functions, such as breathing, heart rate, blood pressure and swallowing.
Pons: Certain neurons in pons Varolii, set higher than the medulla, seem to influence transitions between sleep and wakefulness, and also the rate and pattern of respiration.

Cerebellum: The cerebellum is important in coordinating movements of the body. The cerebellum guides, smooth and accurate motions and body position. The cerebellum is also involved in the learning and memory storage for behaviours. It is best developed in birds, which engage in ‘the complex activity of flight.

SPINAL CORD

Medulla oblongata narrows down into an oval shaped hollow cylinder, the spinal cord, running through the vertebral column. It is made up of a very large number of neurons, the cell fibres and bodies of which are arranged in a definite pattern. In cross section, the spinal cord shows an inner butterfly shaped grey matter, containing a central canal and the outer portion composed of white matter. Gray matter, as in other parts of nervous system consists of  cell bodies and non-myelinated nerve fibres or tracts. White matter, is  made up of myelinated nerve fibres or tracts. The spinal cord is the centre for a great many reflexes and it give out as a passageway for conduction of impulses to and from different parts of the body and brain.

PERIPHERAL NERVOUS SYSTEM (PNS)

It comprises sensory neurons and motor neurons, which may form ganglia and the nerves.
Ganglia: Ganglia are the concentrations of cell bodies of neurons.
Nerves: The nerves are the bundles of axons or dendrites, bounded by connective tissue. They may be sensory, mixed or motor nerves depending upon the direction of impulse they conduct.’ In humans, there are 12 pairs of nerves, which arise from the brain, or lead to the brain these nerves are called cerebral or cranial nerves. Some of these nerves are sensory, some motor, and some are mixed. From the spinal cord, 31 pairs of spinal nerves arise or lead to the spinal cord. All these nerves are mixed i.e., having fibers of both sensory and motor neurons.

SOMATIC NERVOUS SYSTEM

Motor neurons form somatic nervous system, which controls voluntary movements, which are under the conscious control of the body, involving skeletal muscles.

 AUTONOMIC NERVOUS SYSTEM

Motor neurons also form Autonomic nervous system, which controls involuntary responses by influencing organs, glands, and smooth muscles. The autonomic nervous system is further divided into sympathetic nervous system and parasympathetic nervous system. Both of these systems function automatically, innervate all internal organs, utilize two neurons and one ganglion for each impulse.
i) Sympathetic nervous system: Most ganglia of sympathetic system arise from the middle portion of the spinal cord and almost terminate in ganglia that lie near the cord. This system is important during emergency situations and is associated with “fight or flight”. This system accelerates the heartbeat and dilates and inhabits the digestive tract.
ii) Parasympathetic nervous system: A few cranial nerves including the vagus nerve together with fibres from the bottom portion of spinal cord, form the parasympathetic nervous system. It promotes all the inter.nal response which are associated with the relaxed state i.e., contracts of the pupils, promotes digestion. of food, retards heart beat.